Blender is a free open source 3D content creation suite, available for all major operating systems under the GNU General Public License.

Blender  has a superb range of features Blender's animations systems supports a variety of techniques and tasks, allowing the creation of complex animations. You can create 3D models, animation, texturing, rigging characters, and create 3D games.  It has been ported to several operating systems and will run o­n Windows, Linux, and MAC.  Blender also has some advanced simulation and character animation tools.http://www.blender.org/